This invention relates generally to engine braking systems and methods and, more particularly, to a control valve for engine braking systems and methods.
Engine brakes, or engine retarders, are sometimes used to assist and supplement wheel brakes in slowing heavy vehicles, such as dump trucks, construction vehicles, tractor-trailers, and the like. Engine compression brakes convert an internal combustion engine from a power generating unit into a power consuming air compressor. Compressed air from the compression stroke of the engine is released through the cylinder exhaust valve when the piston in the cylinder nears the top-dead-center position. In conjunction with the increasingly widespread use of electronic controls in engine systems, engine braking systems have been developed which are electronically controlled by a central engine control unit.
U.S. Pat. No. 3,220,392 issued to Cummins on Nov. 30, 1965, discloses an engine braking system in which an exhaust valve located in a cylinder is opened when the piston in the cylinder nears the top-dead-center position on the compression stroke. An actuator includes a master piston, driven by a cam and pushrod, which in turn drives a slave piston to open the exhaust valve during engine braking. The actuator is controlled by a hydraulic circuit requiring at least one control valve and at least one solenoid valve for each cylinder.
Thus, the Cummins device requires manufacture, assembly, warranty, and maintenance of these numerous valves. Each of these concerns comes at an expense to the manufacturer and the user. Furthermore, the numerous valves and associated plumbing occupy space in the engine compartment, thus increasing the size of the engine, the weight of the engine, and the gross weight of the associated vehicle.
The present invention provides an economical and reliable engine braking system that avoids one or more of the aforesaid shortcomings in the prior art.
In accordance with one aspect of the invention, an engine braking system for a multi-cylinder engine includes a supply of low pressure fluid and an engine fluid sump. A plurality of valve actuators are each configured to be alternatively fluidly coupled to the supply of low pressure fluid and the engine fluid sump. Each valve actuator is operably coupled to at least one exhaust valve for a respective cylinder. The system also includes a braking control valve operably coupled to two of the valve actuators. The braking control valve is movable between a first position at which the two valve actuators are fluidly coupled to the engine fluid sump and blocked from the supply of low pressure fluid and a second position at which the two valve actuators are fluidly coupled to the supply of low pressure fluid and blocked from the engine fluid sump.
In accordance with another aspect of the invention, an engine braking method for a multi-cylinder engine is provided. Compressed air from the compression stroke of a cylinder is used for engine braking and the compressed air is released through a cylinder exhaust valve near a piston top-dead-center position. The method includes supplying fluid from a supply of low pressure fluid to a braking control valve and selectively controlling movement of the braking control valve between a first position at which two valve actuators are fluidly coupled to an engine fluid sump and blocked from the supply of low pressure fluid and a second position at which the two valve actuators are fluidly coupled to the supply of low pressure fluid and blocked from the engine fluid sump. Each of the valve actuators controls an exhaust valve of a different cylinder.
In accordance with yet another aspect of the invention, an engine braking system for two cylinders of a multi-cylinder engine includes a supply of low pressure fluid, an engine fluid sump, and a valve actuator operably coupled to each cylinder. Each of the valve actuators is configured to be alternatively fluidly coupled to the supply of low pressure fluid and the engine fluid sump. The system also includes a braking control valve operably coupled to two of the valve actuators. The braking control valve is movable between a first position at which the two valve actuators are fluidly coupled to the engine fluid sump and blocked from the supply of low pressure fluid and a second position at which the two valve actuators are fluidly coupled to the supply of low pressure fluid and blocked from the engine fluid sump. A check valve is associated with each of the valve actuators. Each check valve is configured to prevent fluid flow from the respective valve actuator to the supply of low pressure fluid. At least one exhaust valve is operably coupled to each valve actuator.